How to get A. fumigatus in the mood for love A manuscript at Nature AOP details the success of the Dyer lab and collaborators in encouraging Aspergillus fumigatus to complete the sexual cycle under observable (e.g. laboratory) conditions. The authors are the teleomorph (sexual or perfect) stage Neosartorya fumigata for a fungus that had been previously only had an observed anamorphic stage. A. fumigatus can reproduce asexually forming structures called conidiophores which produce asexual spores called conidiospores (or mitospores as they are produced via mitosis) define the anamorph or imperfect stage, but no sexual structures such as cleistothecia that produce the packaged sexual products as ascospores. See a presentation by David Geiser (archived at the Aspergillus website) for more detail on some of the morphological and phylogenetic characters that unify the group of Eurotiales fungi.

Like several other groups of fungi, A. fumigatus was presumed to have a putative cryptic sexual stages inferred from population genetic evidence of sexual recombination, but until no telemorphs had been observed. In addition, an observed perfect stage doesn’t necessarily indicate it is easy to induce mating in laboratory conditions. Complicated media including the ever stressful V8 juice was needed to induce mating in the basidiomycete yeast Cryptococcus neoformans (Erke, J Bacteriol 1976). In fact, Christina Hull’s lab has shown we still don’t even know what ingredients in V8 juice even induce mating (Kent et al, AEM 2008)! Other fungi including Coccidioides have been implicated as cryptically sexual (Burt et al, PNAS 1996) but no one has been able to induce mating in laboratory conditions. In this case a petri plate with a individual of each mating type (since this is a heterothallic fungus), and a series of different media conditions provided an environment suitable for mating to occur.

The work in this paper follows from their previous work identifying isolates of different mating types (Paoletti, Current Biol, 2005). The discovery of sexual stage for Aspergillus fumigatus (which Bret cannot pronounce) is a boon for molecular geneticists in construction of knockout strains and ability to follow recombination. While A. nidulans is a sexual species and model system for genetics, it is useful to have more tools to directly manipulate A. fumigatus and directly test hypotheses about genes involved in pathogenicity.

This observation of meiosis in the laboratory is also is interesting to considered in light of work that RIP is active in other Aspergillus species (and also see this post) suggesting that RIP may be operating under meiotic conditions.

Isolates of different mating types have also been described for the putatively asexual Coccidioiodes (Mandell et al, EC 2007; Fraser et al, EC 2007) so it remains a possibility that we can also induce sexual recombination in laboratory conditions in this fungus.

Céline M. O’Gorman, Hubert T. Fuller, Paul S. Dyer (2008). Discovery of a sexual cycle in the opportunistic fungal pathogen Aspergillus fumigatus Nature DOI: 10.1038/nature07528

3 thoughts on “How to get A. fumigatus in the mood for love”

  1. Hi we are trying to induce sexual stage in Aspergillus spp and would like know the best medium for the purpose.

  2. Did you try what they described in their paper?
    “Aspergillus fumigatus isolates were crossed in pairwise MAT1-1 and MAT1-2 combinations in duplicate on Oatmeal agar medium22 ( Pinhead Oatmeal; Odlum Group) and were incubated inverted at 15, 30 or 45 °C in the dark. Crosses were also established on 2% MEA (Oxoid), Czapek Dox agar and Aspergillus complete medium8 at 30 °C in the dark. Spore suspensions of each isolate (5 105 conidia ml-1) were prepared from seven-day-old cultures. Two 1-l aliquots of each spore suspension were separately inoculated onto the agar surface about 4 cm apart and perpendicular to aliquots of conidia of the opposite mating type. This configuration created four interaction/barrage zones as colonies grew (see Fig. 2a, b). Plates were sealed with one layer of Parafilm. Crosses were examined for cleistothecia periodically over 6 months with Olympus SZH10 Stereo and BX45 light microscopes. “

  3. Hi Reddy,
    If you get in touch with me ( I’ll do my best to help you out.

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